Histochemical detection of glycoconjugates in the inner perivitelline layer of Japanese quail (Coturnix japonica).

The avian inner perivitelline layer (IPVL), a homologous structure to the mammalian zona pellucida, is deposited between the granulosa cells and the oocyte cell membrane during folliculogenesis. In this glycohistochemical study, a panel of fluorescein isothiocyanate (FITC)-labelled lectins was used to characterise and localise the oligosaccharide sequences of the IPVL glycoproteins at different stages of follicular development in the quail ovary. Deacetylation and sialidase digestion were also performed prior to lectin cytochemistry. Contrary to mammals, where the topographical distribution of these carbohydrates is not uniformly distributed throughout the zona pellucida, indicating the regionalisation of oligosaccharide chains, our results demonstrated a homogenous lectin staining of the comparatively thin IPVL. We also found variations in the presence and distribution of the carbohydrate residues in the IPVL during different stages of follicular growth. The IPVL of pre-vitelline follicles distinctly stains with WGA, sWGA and SBA, demonstrating the presence of D-GlcNAc, Neu5Ac and α-D-GalNac in the glycoproteins of the forming IPVL. No staining was found with ConA (specific for α-D-Man, α-D-Glc), LCA (α-D-Man, α-D-Glc), PNA (β-D-Gal-(1-3)-D-GalNAc, VAA (Gal), DBA (α-D-GalNAc(1-3)-GalNAc and UEA-I (α-L-Fuc). With continuing follicular growth of the oocyte and the follicle, this staining pattern changed. LCA and PNA-staining in the IPVL became distinctly positive. As the IPVL of immature oocytes distinctly stains with WGA/sWGA-FITC, but spermatozoa do not bind to immature zona, it appears questionable that carbohydrate residues detected by WGA/sWGA play a major role in sperm-IPVL binding, as suggested in previous investigations.